Performance
Demands | GRP | EPDM | Bitumen Felt |
| Durability | Glass Reinforced Plastic (Fibreglass) is extremely tough (hard) at the expense of flexibility. | Different grades and qualities available. Most systems sold to untrained installers. Edge trims formed by wrapping rubber around pieces of wooden batten. | Bitumen roofing pre-dates the Romans. Succeptible to damage from summer sun and winter frost alike. Edges formed in felt, high failure rate. |
Seam Integrity
/Strength
| The main advantage with GRP, seamless and jointless. | Requires solvent adhered (glued) joints around details, wall flashings, pipe penetrations etc. Easily contaminated during installation - the most common cause of EPDM failure. EPDM 'cures' after installation, becoming stiffer, hard to join/repair. | Hot melted joints - can become soft in sun, and brittle in cold. Unreliable at best. |
| UV Sunlight & Heat Resistance | GRP is highly resistant to UV and can be specified in almost any colour. | EPDM is resistant to UV radiation and heat. | UV exposure breaks down and extracts oils and bitumen from asphalt, eventually it becomes brittle and cracks. Temperature can fall quickly on clear nights causing felt to contract, often tearing/splitting. |
| Reaction to Fire | GRP has some fire resisting properties. | Some EPDM roofing membranes exhibit combustible characteristics. | Poor fire resistance. Built-Up Roofing Systems require aggregates and fire retardant coatings to provide retardancy. |
Vapour Transmission
/Condensation | GRP allows limited vapour transmission. | EPDM allows limited vapour transmission. | Felt allows vapour transmission reducing the risk of condensation. |
Elongation/
Flexibility.
Expansion/ Contraction | GRP will withstand normal building movement through expansion and/or contraction. | EPDM is highly flexible and can cope with building movement. | Felt is not capable of substantial elongation without failure. |
| Appearance | Clean, seamless, sleek in appearance. Can be top coated in most colours. | Rubbery, only available in black, looks dark grey (unless painted white), can fade. | Can look reasonable when new, quickly becomes tatty, cracked, blistered. Stone aggregate ballast washes in to gutters causing blockages and plant life growth. |
| Installation | Produced on site using polyester resin, glass fibre and rollers etc, | Quite simple to install, when properly trained. Requires glued/taped joints, easily contaminated with dirt, moisture and/or old bitumen during installation, leading to early failure. | Applied by gas torch or bitumen boiler, high risk of fire and very expensive insurance premiums. |